This invention relates to emergency descent devices of the type shown in U.S. Pat. No. 530,863 and 516,117 wherein a spool having a cable member wound thereon is retarded in its rotation as the cable member descends by a rotating vane member in a fluid cylinder. More particularly, the invention relates to improvement in such devices and to providing an adjustable bypass for the fluid around the vane member so that the speed of descent can be controlled. The improved device has much broader application than those devices heretofore known for lowering equipment from elevated places such as lowering equipment from a hovering helicopter wherein it is necessary to control the speed at which the equipment is lowered. The improved invention also has application to heavier loads.